Proposal for new pre-merge check: Enforce library layering constraints

[envp]

While working on a recent changeset we realized after a merge that I would end up with a linker error due to a clangBasic -> clangLex edge. It would be nice to statically enforce the library layering constraints before merge.

Current State

Library layering constraints (e.g. clangBasic cannot depend on clangLex) are enforce by the linker after merge.

Desired State

Constraints such as these can be derived from the compile_commands.json and the headers included. Since most headers have standard prefixes llvm/XYZ/..., clang/ABC/..., these can be combined with the linker flags to check if layering constraints are violated or not.

Benefits

1. Enforce explicitly linking against a projectComponent if #include "project/Component/Thing.h" was found.
2. Use the layering constraints to actively guide design.